System for rating electric power transmission lines and equipment

ABSTRACT

A system for determining the current carrying capability of one or more overhead power transmission lines monitors one or more spans of each line on real-time basis and identifies the span having the lowest current carrying capacity which in turn establishes the maximum capacity of the entire line. The thermal state of each monitored line span is determined by measuring the conductor temperature, line current, solar radiation, ambient temperature, and in some cases wind speed and wind direction. These parameters are monitored by a sensor-transmitter unit that may be removably clamped on the line conductor which may range in size from one to several inches in diameter, and includes a radio transmitter for transmitting sensed data to a receiving substation. The data from the sensor-transmitter is multiplexed and transmitted by a telecommunications link to a computer which automatically determines line capacity using the real-time data and also calculates the time required for the &#34;critical span&#34; having the lowest current capacity to reach its maximum safe temperature based on any of a number of step changes in load demands. Each sensor-transmitter may include sensors for monitoring the current level, conductor temperature, solar radiation impinging on the conductor, ambient temperature, wind direction and velocity and conductor sag. These sensors and the transmitter are enclosed in a corona-free housing and are powered by a power supply that includes a transformer core which surrounds and is inductively coupled with the monitored conductor. The core is formed in an upper and lower portion which are shiftable relative to each other upon opening and closing a pair of conductor clamping jaws in order to permit the conductor to be introduced into and withdrawn from the core and to allow the clamping jaws to fit a range of conductor diameters while maintaining constant air gaps between the upper and lower core portions.

This is a continuation of copending application Ser. No. 07/284,967filed on Dec. 15, 1988, now abandoned, which is a divisional ofco-pending application Ser. No. 061,342 filed on Jun. 12, 1987, now U.S.Pat. No. 4,806,855, which is a divisional of application Ser. No.623,842 filed on Jun. 22, 1984, now U.S. Pat. No. 4,728,887.

TECHNICAL FIELD

The present invention broadly relates to electric power transmissionsystems, especially those employing overhead electric power lines, anddeals more particularly with a system for rating the current carryingcapacity of the transmission lines and equipment on a real-time basis bytaking into consideration the thermal effects of line current, windvelocity and wind direction, solar radiation, and ambient temperature onthe line conductor temperature.

BACKGROUND ART

As the load on an electric power system grows, the line currentincreases and energy losses become greater. The load is measured interms of the product of volts and current, or VA. Therefore, in the pastit has been standard practice to increase the voltage level in order tomeet growing demands, thereby lowering the current and minimizing theenergy losses. This approach may be undesirable, however, because of thepotential adverse environmental effects of the higher voltage levels,including high electric fields, radio and television interference,audible noise and induced voltage. If higher voltage levels are notemployed to satisfy increased demands, the remaining options availableto utilities are: increasing the current of the transmission line,employing load management methods and/or encouraging conservation. Ofthese options the only one which has no adverse effect on the consumeror the environment is to increase the current carrying capability of thetransmission line, even though energy losses may increase slightly.

In order to design and effectively utilize overhead electrical powertransmission lines, it is necessary to determine their actual thermalcapacity which in turn determines the maximum amount of electricalcurrent that the lines may safely carry. In the past, design ratings forthe lines have been derived from theoretical calculations based onpessimistic weather conditions and selected values of conductortemperature. The safe values of conductor temperature are based on lineclearance requirements and loss of tensile strength criteria. Weatherconditions substantially affect the current carrying capacity of anoverhead electrical power line. Theoretical calculations are normallybased on assumptions of low wind speeds perpendicular to the conductor,high ambient temperatures and maximum solar radiation, consequently thecalculation for arriving at the design rating is based on the assumptionthat the weather will have a minimum cooling effect on the conductorwhile maximizing the amount of heat absorbed by the conductor. Thisensures that the line temperature will be the highest attainable whenthe line is carrying the rated load in order to prevent the sag of theline from exceeding a preselected safe clearance above the ground, or inorder to prevent the conductor from losing more than the acceptable lossof tensile strength.

It has been found that the conservative theoretical approach describedabove sometimes results in line temperatures greater than the calculatedvalue. Numerous reasons exist for this disparity; for example, in theevent the wind speed is lower than the assumed value, or if the wind isblowing parallel to the conductor, and both the ambient temperature andsolar radiation are greater than the assumed values, then the linetemperature, and consequently the line sag will be greater thanexpected.

In order to obtain more accurate design ratings, some utility companiesin the past have established weather stations at various locations inthe general vicinity of the transmission lines in order to monitor theweather and thus obtain more reliable climatological data which is usedto improve the calculations for arriving at the design ratings. Thisapproach to the problem is less than completely satisfactory for tworeasons. First, the weather information recorded at a single location isnot necessarily representive of the weather along an entire transmissionline. Secondly, since weather is variable in both time and location, itis impossible to accurately calculate how the conductor temperature willrespond to these variable conditions.

It would therefore be desireable to measure the actual temperature ofthe transmission line on a real-time basis, since this would allowrating the line as function of the prevailing weather conditions ratherthan based on assumed pessimistic weather conditions or weatherforecasts. Measuring the actual conductor temperature of the lineprovides two advantages. First, line capacities greater than the designrating are presently available for approximately 90% of the time duringthe year. Secondly, utilities can now predict when a transmission linecannot safely carry the design rated load. A system for directlymonitoring the line temperature and weather parameters and fordetermining the maximum capacity of each transmission line would affordan immediate, low cost, minimum risk solution to a capacity deficiencyproblem which may be particularly acute in areas where there isuncertainty in the load growth rates, public resistance to acquiringrights-of-way for overhead lines and inadequate capital funding.

U.S. Pat. Nos. 4,268,818 and 4,420,752 disclose devices for monitoring,on a real-time basis, the conductor temperature, ambient temperature andline current of an overhead power line. The devices shown in thesepatents required that the conductor temperature sensor be installed atsome distance away from the device so as not affect the measuredconductor temperature. These devices were adaptable only to a relativelysmall range of conductor sizes, without changing the clamp used toattached the device to the conductor line. Since hundreds of differentconductor sizes are currently in service, these devices have limitedapplication in those cases where the transmission line designer desiresto move the device from location to location and install them ondifferent conductor sizes.

As discussed in these prior patents, the load carrying capability of apower line may be restricted by its thermal rating; the thermal ratingis the maximum current the line is capable of carrying and is normallybased on the maximum allowable or safe conductor temperature andassumed, worst-case weather conditions. The starting point inestablishing this rating is to select a safe value of conductortemperature such that the line clearance requirements and loss ofconductor tensile strength criteria are not exceeded.

In establishing the thermal rating, it is necessary to select a safevalue of conductor temperature, which is normally based on clearancerequirements, i.e., the distance from the power line to the nearestpoint on the earth or to an object under the power line. When asteady-state current is applied to a transmission line conductor duringsteady-state weather conditions, the line heats up due to the internalheat generated within the conductor or the I² R losses. This causes theconductor temperature to increase above the ambient air temperature andthe line begins to sag from its original unheated position to a lowerposition, since the length of the line changes. Assuming the line isfixed at each end to a tower or similar structure, the tension will alsodecrease, since the length of the line becomes longer when heated. Thefinal value of the sag that a conductor reaches for a set of weatherconditions and current is important since clearance requirements mustnot be exceeded in order to protect against objects on the ground comingin contact with high voltage lines. Additional factors affecting thefinal sag of the line include mechanical creep and elevated temperaturecreep.

The mechanical creep is a function of time and tension, whereas elevatedtemperature creep is a function of line tension, conductor temperatureand time. Both of these factors also increase the sag of a line. Whenthe initial stringing tension is known, the mechanical creep can bedetermined as a function of time only. Elevated temperature creep is afunction of line tension, conductor temperature and time. Based on theabove, if the conductor temperature is monitored, then the actual linesag or clearance can be determined on real-time basis.

Another factor affecting the choice of the maximum conductor temperatureis the loss of conductor tensile strength as the conductor is heated.For any specific conductor size, type (i.e., ACSR, aluminum, copper,etc.) and stranding, the loss of strength is dependent on conductortemperature and time. The loss of tensile strength is accumulative, thatis, the more the conductor is heated, the greater the loss of strengthand the initial strength is never regained.

As is apparent from the foregoing, all of the factors which limit thecurrent rating to a safe value are a function of conductor temperature.Thus, if the line conductor temperature and weather conditions aremonitored, then the maximum real-time current will be substantiallygreater than the conservative design rating for a large portion of timeduring the year.

A primary object of the present invention is to overcome each of thedeficiencies of the prior approach to establishing the thermal rating ofpower lines. This, and further objects of the invention will becomeclear or will be made apparent during the course of the followingdescription of a preferred embodiment of the invention.

SUMMARY OF THE INVENTION

The present invention provides a system for rating the current carryingcapacity of electrical power lines and associated equipment, andmeasures the temperature of the line, line loading, and related ambientconditions affecting the thermal rating, on a real-time basis. Ratingthe current carrying capacity is achieved by measuring the line current,conductor temperature, ambient temperature and solar radiation for eachportion or span of the line. Having determined the thermal state of theconductor, the maximum current that each span may carry can becalculated.

The system includes four (4) major components:

(1) A plurality of sensor-transmitter units, (2) a receiver, (3) aprogrammed computer, and (4) a transmission line data file. Thesensor-transmitter units are clamped to spans of the power line andsense the temperature of the conductor, and optionally may also senseambient temperature, solar radiation, line current, wind velocity anddirection, and the sag for the associated span on a real-time basis. Thesensed information is transmitted by the sensor-transmitter to areceiving station, and is thence multiplexed via a telecommunicationslink to a programmed computer at an operations center. The transmissionline data file consists of physical, mechanical and electricalcharacteristics of the lines, and line orientations. Using thetransmission line data file, the computer calculates the maximum currentcapacity for each monitored span. The span of the transmission line withthe lowest computed current capacity is identified as the "criticalspan". This critical span is then selected and the resultant calculatedcurrent capacity of such span becomes the maximum transmission linecapacity. Based on any of a plurality of possible load levels, thecomputer projects the length of time it will take the critical span ofeach monitored line to reach its maximum allowable temperature level.

Because of the low probability of low wind speeds at high ambienttemperatures during maximum load levels, thermal ratings obtained by thesystem of the present invention are higher than those derived fromconventional, prior art methods.

Each sensor-transmitter unit consists of a corona free housing, aconductor clamping device, a power supply, one or more parametersensors, one or more signal conditioning circuits, a modulator, an RFtransmitter and an RF antenna. The corona free housing protects theelectronic components installed therein from severe environmentalconditions and high electric and magnetic fields. The housing is at thesame electric potential as the power line, is free of corona and doesnot generate audible noise, or radio or television interference at highvoltages. The unit may be easily clamped on a wide range of sizes ofconductors using an a specially designed, electrically insulated hotstick while the line is energized. The unit is powered from theelectrical energy derived from the power line itself.

The sensor-transmitter unit of the present invention eliminates the needfor obtaining information from remote weather stations. The unitpossesses greater radio transmission range, compared to prior artdesigns, is relatively small in size and is light weight. The systemprovides numerous other benefits and advantages. For example, use of thepresent system by electric utilities provides much high thermal linecapabilities and has a significant impact on deferring the building ofnew system facilities. Because of the thermal time lag of the conductorline, short duration emergency ratings well in excess of steady stateemergency ratings may be achieved because the actual conductortemperature, line loading and weather conditions are known.

The system may be extended to include other limiting elements of thepower system such as terminal equipment, power transformers, etc., andthereby provides an increase in those ratings which ordinarily limit theline loading.

Since the actual conductor temperature of the transmission line isknown, system operations during normal and emergency conditions will beimproved with reduced system risk.

In the past it has been common to estimate the conductor loss ofstrength and sag based on an assumed conductor temperature-time model. Aquestion existed as to how accurate the model was compared to the actualoperating temperature; the present system can be used to create morerealistic thermal models which in turn result in an accuratedetermination of the sag and loss of conductor strength.

The present system may be employed to compute line resistance and energylosses more accurately.

It is often difficult to arrange shut downs of certain lines due toother lines being loaded over their emergency rating. Use of the presentsystem will substantially reduce the need for these types of shut downs,thereby resulting in economic savings since power generation does nothave to be rescheduled. The present system allows determination of theinternal temperature gradient of the conductor line, and the effect thetemperature gradient has on sag. Since the thermal state of theconductor is known, the present system may be used to predict the timean overload can remain on a line before reaching its safe limitingconductor temperature.

Risk curves which indicate the precent of time the real-time rating isabove or below the conventional rating are available from the programsforming a part of the present system, and these curves provid the degreeof risk that system operators take by exceeding any preset rating level.

The present system thus provides an indication of the risk for each loadlevel on the transmission line, thereby allowing an operator to exercisebetter judgement in selecting different load levels for each line,depending upon the importance of each line segment in maintaining theintegrity of the transmission network.

Finally, the present system may be employed to prevent ice formation onoverhead power lines. Since the conductor temperature is measured by thesensor-transmitter unit, the current can be increased so as to maintainthe conductor temperature greater than 32 degrees F.

These, and further features and advantages of the present invention willbe made clear or will become apparent during the course of a detaileddescription of the system set out hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which form an integal part of the specification and areto be read in conjunction therewith, and in which like referencenumerals are employed to designate identical components in the variousviews:

FIG. 1 is an upper perspective view of the sensor-transmitter of thepresent invention, during installation thereof on an overhead power lineand also depicts tools for lifting the sensor-transmitter unit onto theline and clamping the unit on the line;

FIG. 2 is a side elevational view of the sensor-transmitter shown inFIG. 1, with the jaws in a closed, clamping position;

FIG. 3 is a front view of the sensor-transmitter unit, parts of thehousing being broken away in section to reveal the means forinterconnecting the two halves of the unit;

FIG. 4 is a top plan view of one form of the sensor-transmitter unitemploying a solar radiation sensor;

FIG. 4a is an enlarged sectional view taken along the line 4a--4a inFIG. 4;

FIG. 4b is an enlarged top plan view of the solar radiation sensor shownin FIG. 4;

FIG. 5 is a sectional view taken along the line 5--5 in FIG. 2;

FIG. 6 is a view of the interior of one half of the housing of thesensor-transmitter unit, the internal parts having been removed tobetter reveal the internal compartments thereof;

FIG. 6a is an enlarged, longitudinal sectional view of the solarradiation sensor shown in FIG. 4;

FIG. 7 is a sectional view taken along the line 7--7 in FIG. 6;

FIG. 8 is a sectional taken along the line 8--8 in FIG. 2, several ofthe electrical circuits and the jaw opening and closing mechanism havingbeen removed for clarity;

FIG. 9 is a sectional view taken along the 9--9 in FIG. 2, the jawopening and closing mechanism having been removed for clarity;

FIG. 10 is a view similar to FIG. 6, but showing the various internalcomponents, with the right side of the housing removed and alsodepicting one form of the power transformer core;

FIG. 11 is a sectional view taken along the line 11--11 in FIG. 2 and10;

FIG. 12 is a side elevational view of the upper and lower portions ofthe transformer core shown in FIG. 10, removed from thesensor-transmitter unit;

FIG. 13 is a detailed, side elevational view of the jaw opening andclosing mechanism of the sensor-transmitter unit shown in FIG. 10;

FIG. 13a is a sectional view taken along the line 13a--13a in FIG. 13;

FIG. 14 is a front elevational view of the mechanism shown in FIG. 13;

FIG. 15 is a side elevational view of the sensor-transmitter unit withone half of the housing removed, and showing an alternate form of thetransformer core;

FIG. 16 is a front view of the jaw opening and closing mechanism shownin FIG. 15;

FIG. 17 is a sectional view taken along line 17--17 in FIG. 16;

FIG. 18 is a fragmentary, elevational view similar to FIG. 15 butshowing another form of the antenna employing means for sensing thedirection and velocity of the wind;

FIG. 19 is a sectional view taken along the line 19--19 in FIG. 18;

FIG. 20 is a sectional view taken along the line 20--20 in FIG. 18;

FIG. 21 is a sectional view taken along the line 21--21 in FIG. 20;

FIG. 22 is a detailed, sectional view of the mounting arrangement forthe conductor temperature sensor;

FIG. 23 is a side elevational view of the jaws showing the relativeplacement of the temperature sensors;

FIG. 24 is a fragmentary, longitudinal sectional view taken throughpower supply transformer coil;

FIG. 25 is a fragmentary, sectional view of the upper portion of analternate form of the sensor-transmitter unit which does not employ aninclinometer for measuring sag;

FIG. 26 is a combined block and schematic diagram of a circuit employedin the sensor-transmitter unit for sensing wind velocity and direction;

FIG. 27 is a block diagram of the electrical circuit employed in thesensor-transmitter unit;

FIG. 28 is a diagrammatic view showing the circuit components which aremounted on the cover plates of the sensor-transmitter unit;

FIG. 29 is a diagrammatic view of a 40 mile power line employing thesystem of the present invention;

FIG. 30 is a block diagram of the broad components of the system of thepresent invention; and

FIG. 31 is a flow chart for the software employed by the programedcomputer which forms part of the system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a system for rating the current carryingcapacity of electrical power lines and associated equipment, whichmeasures the temperature of the line, line current, and related ambientconditions affecting the thermal rating, on a real-time basis. Beforeturning to a description of the details of the system it is important toappreciate how the thermal state of a power line conductor can bedefined by measuring only the ambient temperature, conductortemperature, solar radiation and line current.

Under steady state conditions, the current flow in an electricalconductor may be defined by the following equation, ##EQU1## where Q_(c)is the convected heat, either free convection or forced convection,Q_(r) is the thermal radiation, and Q_(s) is the solar radiationabsorbed by the conductor. Equation (1) represents a heat balanceequation, that is, the internal heat generated within the conductor, orI² R, plus the heat gained from the sun must be equal to the heat lostby thermal convection and thermal radiation. The current may be foundfrom equation (2) if Q_(c), Q_(r), Q_(s), and R, the resistance as afunction of conductor temperature t_(c), are known.

The heat transfer rate Q_(c) is defined by the equation

    Q.sub.c =hA(t.sub.c -t.sub.a)                              (3)

where h is the surface coefficient of heat transfer, A is the surfacearea of the conductor per unit length, t_(c) is the surface temperatureof the conductor and t_(a) is the ambient air temperature. If thesurface conductor temperature and ambient air temperature are measuredor monitored and the outside conductor diameter D₀ is given, then theconvected heat Q_(c) can be calculated once h is determined. It isapparent that the convected heat, either forced or free, could beobtained directly under steady state conditions from equation (1), ifthe other three heat quantities are known. If the current, conductortemperature, ambient temperature, and solar radiation are measured thenthe convected heat is the only remaining quantity in equation (1).

The current, an electrical quantity, does not change in magnitude as afunction of position along the conductor line therefore it may measuredat the termination of the line with no loss of accuracy. The otherquantities must be measured on the line because they vary due tovariable ambient conditions along the line. The first term in equation(1), that is, the internal heat I² R, can be found by measuring thecurrent and calculating the resistance from the measured conductortemperature. Therefore, the I² R losses at any point along the line canbe computed directly from the measured current of the line and theconductor temperature at each point along the line.

The other two terms in equation (1) are the solar radiation absorbed bythe conductor Q_(s), and the thermal radiation Q_(r). The amount ofsolar radiation absorbed by the conductor can easily be determined,given the solar absorption constant, conductor size and orientation,beamed radiation Q_(B), diffuse radiation Q_(D), and time. Although thequantities Q_(D) and Q_(B) can be measured, it is more convenient tomeasure the solar radiation on a horizontal surface and calculate thebeamed and diffuse radiation components.

If the conductor temperature t_(c), and the ambient temperature t_(a)are measured and the physical properties of the conductor, emissivity E,and the conductor diameter D_(o) are given, then Q_(r) can becalculated.

When the I² R losses at any point along the line, and Q_(s) and Q_(r)are calculated, Q_(c) becomes the only unknown term in equation (1), or

    Q.sub.c =I.sup.2 R+Q.sub.s -Q.sub.r,                       (4)

and h can be found from equation (3), ##EQU2##

Notice that the only measured quantities needed in arriving at theconvected heat are the current, conductor temperature, ambienttemperature and solar radiation.

Once the thermal state of the conductor or h has been defined, themaximum real-time current that any one segment of a transmission linecan carry is easily determined by substituting the maximum allowableconductor temperature for the line segment, and the measured ambienttemperature and solar radiation values into equation (2). The resistanceR is evaluated at the maximum allowable conductor temperature. It couldbe said that the measured quantities t_(c), t_(a), I, and Q_(s), havedefined the "now" thermal state of the conductor, and equation (2) givesthe maximum real-time current that could flow such that the maximum safeconductor temperature is not exceeded. This presumes that the thermalstate does not change over a short time interval, and of course this istrue because the conductor has an associated thermal time constant. Thisalso infers that the conductor temperature and current must be monitoredat small intervals of time. In general, the conductor temperature willbe operating at a level well below that which would cause the line toexceed clearance and loss of strength requirements, because theconservative thermal rating or current for the line historically hasbeen based on low wind speeds and high ambient temperatures. Therefore,the real-time current carrying capacity will be considerably higher thanthe design rating.

There have been a number of references hereinabove to the fact that thethermal state of the conductor is known at a point or at a line segment,since atmospheric conditions could vary substantially along the entirelength of a transmission line. This is true because thesensor-transmitter measures the conductor temperature, ambienttemperature, and solar radiation at a point on the conductor and,therefore, these conditions are representative of those existing on asegment of line or a span of the line. In order to extend the concept ofthe present invention to the entire line, it is necessary to install asufficient number of sensor-transmitters, so that these conditions areknown for each portion of the transmission line. Normally, not more thanone sensor is needed for each span, since the line cannot changedirection within the span.

Referring now to FIGS. 1-3, the present invention involves a system forrating the thermal or current carrying capacity of overhead electrictransmission lines, and employs a sensor-transmitter unit generallyindicated at 30 for monitoring certain parameters used in calculatingthe thermal rating of the lines. The unit 30 includes a housing 34adapted to be removably clamped to a current carrying conductor, such asthe overhead power line conductor 32. The housing 34 includes first andsecond halves 34a and 34b secured together by a plurality of machinescrews 56. The four upper machine screws 56a are provided withinsulative bushings and washers 56b, 56c in order to electricallyisolate the upper portions of the housing halves 34a and 34b.

The housing 34 is generally "C-shaped" in geometry and comprises asubstantially rectangular base 35, an upwardly extending rear column 40,and forward upper extension 42 which includes a downwardly turned nose44. The upper extension 42 and nose 44 are spaced above the base 35 todefine and opening or passageway 37 through which the conductor 32 maybe passed during installation or removal of the unit 30 from theconductor 32. The passageway 37, which facilitates installation of theunit 30 on the conductor 32, is selectively opened and closed by a laterdiscussed opening and closing mechanism.

The exterior surface of the housing 34 is formed in a manner toeliminate sources of corona when the unit 30 is installed on highvoltage transmission lines. The housing 34 may be formed by casting azinc and aluminum alloy material, by forming sheet aluminum using a deepdraw die or from an epoxy-like substance including an aluminum binder orfrom aluminum using a sand casting process. Preferably, the housing 34is formed from an aluminum alloy and is vapor blasted or burnished toensure a smooth, corona free surface and is anodized to reduceoxidation.

Stationarily mounted on the housing 34, and extending into thepassageway 37 are a pair of upper stationary jaws 50 each provided withan arcuately shaped or radiused jaw surface 51 having a curvatureessentially identical to that of the largest diameter conductor 32 onwhich unit 30 is intended to be mounted. A lower, reciprocable jaw 52 ismounted within the housing 34 by a later discussed mechanism, andincludes an arcute or radiused jaw surface 53 having a curvaturesubstantially equal to that of the smallest diameter line 32 in therange which the unit may be installed upon.

A radio antenna generally indicated at 13 defined by a cylindricalantenna tube 46 formed of aluminum or the like is secured to and extendsdownwardly from an antenna base 45 on the bottom of the housing 34. Ametal sphere 48 is secured around the lower end of the tube 46 andfunctions to prevent the antenna from producing corona. The tubeincludes an opening 76 (FIG. 8) therethrough into which a tool 166 maybe inserted for opening and closing the jaw 52 relative to jaws 50. Thetool 166 is secured on the end of a hot stick 172 (insulated rod shownin FIG. 1) and includes a horizontal groove 168 on the end thereof aswell as a longitudinal extending slot 170.

As best seen in FIG. 3 the upper jaws 50 are spaced apart from eachother and engage the conductor 32 on opposite sides of the point atwhich the lower jaw 52 engages the conductor 32.

Attention is also now directed to FIGS. 5 through 9 wherein the interiorfeatures of the housing 34 are depicted in more detail. The interiors ofthe housing halves 34a, 34b, respectively, include a plurality ofcompartments for protectively enclosing various components from both theenvironment and the electric and magnetic fields respectively producedby the voltage on the conductor 32 and the current flowing throughconductor 32. A pair of substantially rectangular compartments 58 and 60are respectively defined in the rectangular base portion of housinghalves 34a and 34b. The compartments 58, 60 are sealed off from theenvironment and electric as well as magnetic fields by a pair ofcorresponding cover plates 62, 64 which may optionally include louvers68 permitting air to enter the corresponding compartments. Cover plates62, 64 are spaced apart to define central opening 65 in housing 34within which there is contained a later discussed jaw opening andclosing mechanism (FIGS. 13, 14, 16 and 17). Later discussed electroniccomponents and/or circuit boards are mounted on the inside faces of thecover plates 62, 64, while the exterior faces of plates 62, 64 provide asurface for mounting guide tracks 66 which aid in confining the travelof the jaw opening and closing mechanism in a vertical direction. It maythus be appreciated that ready access may be gained to the compartments58, 60 for servicing the electronic components simply by removing thecover plates 62 and 64. The cavity 116 internal of the column 40provides a compartment for two electrolytic power supply capacitors anda portion of a later discussed upper magnetic core portion 102.

It should be noted that the cover plates 62, and 64 are preferablyformed from ferrous material which shields the electronic componentsfrom magnetic fields around the conductor 32. Additionally, the positionof the compartments 58 and 60 spaces the electronic components as faraway from the conductor 32 as possible to reduce the influence ofmagnetic fields. The cover plates 62, 64 are secured within recesses inthe housing halves 34a, 34b and further function to provide the housing34 with rigidity which tends to resist the torque applied to housing 34when the jaws 50, 52 are closed by the tool 166.

As best seen in FIGS. 7 and 11, the upper extension 42 of the housingincludes a central power supply compartment 42a formed by matingcavities in the housing halves 34a, 34b, and a pair of temperaturesensor compartments 42b and 42c. The laterally spaced apart temperaturesensor compartments 42b and 42c are closed off from the power supplycompartment 42a by a pair of corresponding cover plates 96, 98.

The power supply for the unit 30 comprises a later discussed transformercore 102, and a transformer coil 100 which is mounted in the powersupply compartment 42a which is positioned as far away from theconductor 32 as possible so that the heat generated from the powersupply does not affect the temperature of the conductor 32. Thermalconduction from the core 102 and coil 100 to the conductor 32 is furtherreduced by air space 43 (FIG. 25) beneath the coil 100 and floor 142 atthe bottom of the compartment 42a. Cover plates 96 and 98 function toseal the temperature sensor compartments 42b, 42c and strengthen thehousing around those compartments. A portion of the floor 142 may beremoved as shown in FIGS. 8 and 15 in order to mount an inclinometer 84for measuring the sag of the conductor 32.

Located in compartment 42b is a temperature sensor 88 in the form of atransducer for sensing the temperature of the conductor 32. A secondtemperature sensor 86 is mounted in compartment 42c for sensing theambient temperature or another conductor temperature. The number ofconductor temperature and ambient temperature sensors that may beinstalled in the upper and lower jaws 50, 52 will depend upon theoverall system reliability that is desired. In the event that only oneconductor temperature sensor is used, the ambient temperature sensor 86is typically installed in the right upper clamp (FIG. 8). The ambienttemperature sensor 86 is located a distance away from the conductor 32so that temperature measured is the same as the outside ambienttemperature. For conductors larger than one inch in diameter, forexample, the ambient sensor 86 is not mounted directly over theconductor 32, but rather is mounted in the right jaw 50 near the column40, as shown in FIG. 23. The ambient temperature 86 may also beinstalled in the lower jaw 52 if desired. In any event, all three of thejaws 50, 52, are normally shaded so that direct sunlight does not heatthe jaws. Mounting the ambient and conductor temperature probes in thethermally insulating material of the jaws avoids heating of the probesby direct sunlight on the probes and direct sunlight on the unit 30.Consequently, direct sunlight does not affect the measured ambient orconductor temperatures.

As best seen in FIGS. 22 and 23, the conductor temperature sensor 88 ismounted on the floor of the temperature sensor compartment 42b andincludes an elongate probe 92 which extends downwardly through anopening in the floor and through the jaws 50 where the conductor 32 isclamped. The probe 92 is reciprocally mounted for travel into and awayfrom the opening between the jaws 50, 52 by means of a spring 90 whichis sleeved over the probe 92. The spring 90 is held between the teflonsleeve 93 and a threaded fitting 89. The mass of the probe 92 shouldpreferably be made small with respect to the mass of the conductor 32 orconductor strands. To increase the contact surface and provide a moreuniform contact over the entire end of the magnetically shielding probe92, while making the mass as small as possible, a small aluminum shoe 95is heat shrunk over the outer end of the probe 92. The high interferencefit created by heat shrinking the aluminum shoe 95 eliminates atemperature drop which would otherwise occur if a thin air film werepresent between the shoe 95 and the probe 92. The shoe 95 is providedwith a partially cylindrical bottom surface 97 which approximates thecurvature of the conductor 32 and is intended to conformally engage theconductor 32. Shoe 95 may be plated on the outside with silver orcadmium for use on copper and aluminum conductors 32, so that galvaniccorrosion, caused when different metals are in contact with each other,does not occur.

To further minimize temperature sensing error produced when heat isconducted from the conductor 32 up through the probe 92, a thermalconstriction is provided immediately above the top of the shoe 95; thethermal constriction is formed by a pair of slots 99 in the outersurface of the probe 92. The slots 99 define a relatively small amountof probe material therebetween which in effect restricts the amount ofheat that can flow upwardly through the probe 92. In order to compensatefor any reduction in strength of the probe 92 as result of the slots 99,a tube 93 of material having a low thermal conductivity, such as teflonis formed around the probe 92. A spring clamp 91 retains the spring 90on the probe 92. The spring 90 biases the probe 92 downwardly intocontact with the conductor 32. Heat loss from the shoe 95 to the ambientenvironment is minimized by concealing a substantial portion of the shoe95 and the probe 92 within the thermally insulating jaw 50 when theprobe 92 is depressed by the conductor 32.

The leads of the temperature sensing transducer 95a are preferablymagnetically shielded with stainless steel tubing 94 or the like. Theconductor temperature sensor 88 may comprise a standard typethermocouple available from Omega Engineering Inc. The temperaturesensor 88 is preferably modified, however, to reduce the error inmeasuring the temperature of the conductor strands. The ambienttemperature sensor 86 may consist of a standard thermocouple orintergrated circuit transducer. As previously discussed, in order toincrease the contact surface and provide uniform contact over the entireend of the probe 92, while making the mass as small as possible, a smallaluminum shoe is heat shrunk over the tip of the probe 92. A highinterference fit is created by heat shrinking the aluminum shoe to thethermocouple probe 92; this eliminates a drop in the temperature thatwould otherwise exist if a thin air film were present between thealuminum shoe and the probe 92. Typically, the aluminum shoe on theprobe 92 will contact two or more strands of the conductor 32.Additionally, thermal constriction slots must be added to the probe toreduce heat from being conducted from the conductor 32 up through theprobe and a teflon sleeve is installed around the probe to compensatefor loss of strength in the probe due to the constriction slots addedtherein.

In lieu of the thermocouple, the temperature sensor 88 may comprise anintergrated circuit temperature transducer which is commerciallyavailable from Analog Devices and is identified by the manufacturer'sNo. AD 590.

The bottom of the housing 35 is provided with a water well 115 formedbetween the housing halves 34a, 34b in order to collect any water whichmay gain access to the interior 65 of the housing 35, between the twohalves thereof. A drain hole 114 in the bottom of the housing 35communicates with the well 115 in order to drain away the water. Fourholes 67 are provided in the bottom of housing half 34a (FIG. 9) inorder to provide ready access to zero and span adjustments for theambient and conductor temperature signal conditioning circuits; thesesame holes assist in draining condensation which accumulates within thehousing half 34a and provide ventilation paths from the bottom of thecompartment 58 to the top of the housing and out through horizontalventilation slot 110. A drain hole 67a is also provided to draincondensation from the inside of housing half 34b and provide aircirculation from the bottom of compartment 60, and out through slot 112.A pair of drain holes 300, 302 are provided in the floors of thetemperature sensor compartments 42b, 42c in order to drain condensationtherefrom (FIG. 11).

A pair of diverter plates 78a, 80b are mounted on the interior wallsdefining the compartments 58, 60 and function to divert ventilation airoutwardly through the ventilation slots 110, 112 (FIG. 8).

The nose 44 of the housing 35 includes a wide, flat sloping surface 121on the bottom thereof to assist in guiding the conductor 32 through andinto the opening 37. A cylindrical opening 120 in the sloping surface121 is provided to allow entry therein of a later discussed core coversleeve 36. As best seen in FIG. 2, with the jaws 50, 52 closed, thesleeve 36 and nose 44 enclose the overlapped extremities of the coreportions 102, 104 of FIG. 10. The cover sleeve 36 functions to protectthe lower core portion 104 from the surrounding environment and providesa smooth conducting surface around the core portion 104 so that it willnot become a source of corona in the high electric fields of the highvoltage power line 32. As seen in FIG. 13a, the lower core portion 104occupies a space on the left side of the center line of the cover sleeve36. This arrangement allows the upper core portion 102 to occupy thespace adjacent to the lower core portion 104 on the right side of thecover sleeve center line. As best seen in FIG. 14 the cover sleeve 36includes notches 137 at the top thereof dimensioned to assure that anoverlap of approximately 0.5 inches in maintained between the upper andlower core portions 102, 104, respectively.

As seen in FIGS. 8, 11, 14 and 25, an isolation slot 144 is providedbetween the upper portion of the two halves 34a, 34b of the housing 34,which extends up through the inside of sleeve 36 to the inside of thecolumn 40 and through the floor 42 of the power supply compartment 42a.Thus, the isolation slot 144 effectively circumscribes the conductor 32.Slot 144 electrically isolates the upper portions of the housing halves34a, 34b from each other and therefore prevents the housing from actingas a low impedance turn of wire around 102, 104, thus preventing currentfrom circulating around the housing and core and shorting the powersupply transformer coil 100. This slot 144 may be formed by removing anappropriate amount of material from the opposite faces of upper portionsof the housing housing halves 34a, 34b and installing a suitableinsulating washer 303 (FIGS. 10 and 11) therebetween at the front of thehousing and an insulating gasket 304 at the rear thereof. The slot inthe cover sleeve 36 may be filled with a suitable insulating material306 (FIG. 13a). Note in FIG. 14 there is also provided an isolation slot144 between the back clamping plate 153 and core retainer 136, and abovethe lower core portion 104. Also, as shown in FIG. 17, an isolation slot144 is provided between the back clamping plate 153 and the coreretainer 136.

It should be noted that the geometry of the housing 34 and the weightdistribution of the components of the unit 30 are arranged such that thevertical axis of the unit 30 (and thus the longitudinal axis of theantenna 13) remains vertical when the unit is installed on the conductor32. Also, the center of gravity of the unit 30 lies below the conductor32, thereby providing damping action to the torsional motion of theconductor 32 during high wind conditions and mitigates conductorgalloping.

Bundle conductors, consisting of two or more conductors per phase, aresometimes used on high or extra high voltage transmission lines. Thelateral distance between the center line of the conductor and theoutside surface of the installed unit 30 is only approximately 5 inches.Because of this compact design, the unit 30 may be installed near thebundle spacer on one of the conductors of a twin conductor bundle, or onone of the lower conductors of a four conductor bundle arrangement, andadequate clearance is maintained between the unit 30 and any adjacentconductors.

Attention is also now directed to FIGS. 13, 13a and 14 which depict thelower jaw 52 as the well as the details of the opening and closingmechanism for the jaw 52. The jaw or clamping arrangement of the presentinvention is designed to prevent the heat sink effect that most metallicconductor clamps have on an overhead transmission line conductor and toassure that the unit 30 remains tight on the conductor 32 even thoughthe differential thermal expansion of the housing 34 is much greaterthan that of the steel lead screw 138 which firmly holds the conductor32 between jaws 50, 52.

The jaws 50, 52 are preferably constructed of a thermally insulatingmaterial that will operate satisfactorily at 400 degrees F. (240° C.).When unit 30 is installed on the conductor 32, the upper jaws 50 supportthe weight of the unit 30. The recessed jaw surface 51 in the jaws 50holds the unit 30 in place and prevents the unit from rotating while thetool 166 is being used to tighten the unit on or remove the unit fromthe conductor 32. The unit 30 is precluded from rotating due to the factthat the upper jaws 50 are spaced apart and also because of the recessedconductor engaging surfaces of the upper jaws 50. The unit 30 is clampedon the conductor 32 by turning the lead screw 138 using the tool 166which is inserted into the antenna tube 46. The lower end of the leadscrew 138 is provided with a suitably configured key in the form of atransverse pin 137 which is mateably received within the horizontalgroove 168 of tool 166. The groove 168 provides a means of turning thepin 137 and lead screw 138, and remains engaged with the pin 137 whilethe lead screw is being turned clockwise consequently a constant upwardforce need not be applied to the tool 166. As will become laterapparent, the unit 30 is clamped onto the conductor 32, the conductortemperature probe is attached to the conductor 32, and the unit's powersupply is turned on in a single step when the lead screw 138 tightensthe jaws 50, 52 onto the conductor 32.

The unit 30 is clamped on the conductor 32 by turning the lead screw 138until the lower jaw 52 is secured to the conductor 32. In order totighten the jaws securely, a torque of between 25 and 40 pounds for 1 to2 inch diameter conductor lines is required. Because the conductor 32 isheld at the top by two spaced apart jaws 50 and at the bottom with lowerjaw 52 which is located centrally between the upper jaws 50, theconductor 32 is deflected slightly into a concave downward attitude. Theconductor 32 does not take on a permanant set from the jaws 50, 52, butrather acts like a spring placed between the two upper jaws 50. Thisspring like action compensates for the difference in thermal expansionbetween the steel lead screw 138 and that portion of housing 34 to whichthe lead screw 138 is secured by means of a lead nut 70 (FIG. 10). Sincethe upper and lower jaws 50, 52 create a small moment on a section ofthe conductor 32, the unit 30 cannot slide or swing back and forth alongthe axis of the conductor 32.

The clamping arrangement of the present invention also avoids thephenomena known as conductor bird-caging because the temperature of thestrands of the conductor 32 under the jaws 50, 52 is the same as thetemperature outside the jaws. Bird-caging of the outside surface strandsof a conductor, or the spreading out of the strands in a radialdirection away from the inner strands of the conductor, is a result ofthe strands under a metallic conductor clamp being at a lowertemperature than those adjacent to the clamp and exposed to the ambientenvironment. In any event, this phenomena is avoided by staggering theplacement of the jaws 50, 52 on the conductor 32, by providing as muchair space as possible around the conductor 32, by minimizing the area ofthe jaw in direct contact with the conductor 32 and by using jawmaterial of an appropriate insulation thickness with low thermalconductivity. Spacing of the jaws 50, 52 relative to each other createstwo radial air spaces on each side of the lower jaw 52. Additionally,the surface area of the conductor 32 directly below the upper jaws 50and the above the lower jaw 52 is completely open to the ambientenvironment. Because the temperature of the conductor 32 under the jaws50 is essentially the same as the undisturbed line temperature, anaccurate measurement of the conductor temperature is achieved.

Each upper jaw 50 is mounted between an outer drip rail 128, 130 and aback plate 178 (FIG. 8). The drip rails 128, 130 function to preventwater from entering the interfacing area between the top of the jaws 50and the underside of the floor of the temperature transducercompartments 42b, 42c. The back plate 178 functions to restrict movementof the jaws inwardly when lower jaw 52 is tightened against theconductor 32. The upper jaws 50 are secured to the housing 34 by machinescrews or the like extending through the drip rails 128, 130. The backplate 178 is preferably formed of an insulating material such as nylonand provides a number of functions in the present invention. First, theback plate 178 assists in guiding the jaw opening and closing mechanism(FIGS. 13 and 14) and prevents the conductor 32 from being nicked whenthe unit 30 is installed on the conductor 32. It should be noted herethat it is preferable to "slam" the unit 30 onto the conductor 32 duringinstallation in order to prevent arcing therebetween. Additionally, thebacking plate 178 prevents water from entering the column 40 and intothe air gap between the core portions 102, 104. Finally, the insulativeback plate 178 prevents thermal conduction from the conductor 32 to thehousing 35 when the unit 35 is clamped onto larger conductors (See FIG.10).

The jaw opening and closing mechanism best seen in FIGS. 13 and 14 iscontrolled by the hot stick operated tool 166 in order to clamp the unit30 onto an energized conductor 32, to close the magnetic circuit of thepower supply transformer which in turn powers the electronic circuits ofthe unit 30 and to attach the conductor temperature sensors on thesurface of the conductor 32.

The jaw opening and closing mechanism includes a clamping block 132secured to the upper end of the lead screw 138 and a retainer plate 133secured to the mounting block 132 by means of machine screws. The lowerjaw 52 is secured to the clamping block 132 by means of a pair ofclamping plates 129, 131. The lower portion 104 of a J-shaped coreportion has an intermediate section extending between the clampingplates 129, 131 and is secured to the clamping block 132 by means of acore retainer 136 and set screw 136a. The core cover sleeve 36 issecured to the clamping block 132 by means of a connecter plate 134which is connected as by welding to the sleeve 36.

The jaw opening and closing mechanism shown in FIGS. 13 and 14 isreceived within the open space indicated at 65 in FIG. 9 between thecover plates 62, 64 and is confined for vertical reciprocal movement bymeans of the guide tracks 66 shown in FIG. 10. Note that an open airspace is provided below the jaw 52 and between the two clamping plates129, 131; this space provides a high thermal resistivity path from theconductor 32 to the ambient air, and thus the heat thermally conductedaway from the conductor 32 in the lower jaw area is negligible. Thishigh thermal resistivity path is due to several reasons. First, thelower jaw 52 consists of a thermal insulating material of low thermalconductivity. Secondly, there is air space provided below the jaw 52.Finally, the back plate 178 is formed of a thermally insulatingmaterial. There is also an air space provided between the lower jaw 52and the core cover sleeve 36. Thus, the conductor 32 is either in directcontact with the ambient air, or is in contact with a very small area ofthe jaws 50, 52 which in turn, have very high thermal resistivity pathsto the housing 34. This design ensures that the surface temperature ofthe conductor 32 is not affected by the presence of the unit 30 mountedon the conductor 32.

The clamp block 132 is offset slightly relative to the center line ofthe conductor 32 in order to achieve proper weight distribution whichmaintains the unit vertical when clamped on the conductor 32.

The lower jaw 52 is held place between the clamping plates 129, 131using a pair of screws 306, 308. One screw 306 enters through the frontclamping plate 129 and into the jaw 52 while the other screw 308 extendsthrough the back clamping plate 131 and into the jaw 52. If the screws306, 308 extended through the front clamping plate 129, through the jaw52 and into the back clamping plate 131, a circulating current wouldflow around the core defined by a path consisting of the clamping block132, the clamping plates 129, 131 and the screws 306, 308.

As best seen in FIG. 10, the upper jaws 50 are sized to fit the largestconductor within a particular range of diameters, while the lower jaws52 are sized to fit the smallest conductor in the range. For example, ina unit adapted to clamp onto 1 to 2 inch conductors the upper jaw wouldpossess a recessed surface 51 having a 1 inch radius and the lower jaws52 posses a recess surface 53 having a 1/2 inch radius.

The upper jaws 50 include a sloped surface 55 which facilitates slidingof the conductor 32 into recessed surface 51 during installation of theunit 30 on the conductor 32, and also protects the conductor temperatureprobe 92 from being contacted on the side by the conductor 32. Theconductor 32 slides down sloped surface 55 and is directed beneath thelower extremity of the temperature probe 92. The temperature probe 92 iseasily pushed upwardly by the conductor 32 if the conductor 32 firstcontacts the probe 92 on the bottom, rather than on the side.

The radial thickness of the jaws 50, 52 is preferably selected such thatthe heat loss for the bare conductor 32 is the same as the heat loss forthat portion of the conductor 32 under the jaws 50, 52. This optimumcondition is also facilitated by the fact that the jaws 50, 52 arestaggered relative to each other. This arrangement provides the maximumamount of the conductor 32 to be exposed to the ambient conditions.Additionally, the jaws 50, 52 must be able to withstand a surfaceconductor temperature ranging from 125° C. to 175° C. on a continuousbasis, have a high compressive strength and low coefficient of thermalexpansion, exhibit low flammability and water absorption and display areresistance characteristics. One material suitable for this purpose isTeflon FEP. Since the conductor temperature probe 88 is grounded to theconductor 32 or is at the same electrical potential as the conductor 32and its shield is grounded to the housing 35, the dielectric strength ofthe jaw material is relatively unimportant. Clearance is providedbetween the upper and lower jaws 50, 52 in order to allow for a certainamount of "crush" (the conductor 32 becomes somewhat eliptical in shapewhen the jaws 50, 52 are tightened).

The electrical components of the sensor-transmitter unit 30 are drivenby a power supply which derives power from the electromagnetic field ofthe monitored transmission line conductor 32. The power supply comprisesthe two identical, nested "J" shaped magnetic core portions 102, 104(FIG. 12) previously discussed and the coil 100. The upper core portion102 is inverted with respect to the lower core portion 104 and isfixedly secured to the housing half 34b. One set of extremities of eachcore portion 102, 104 are radiused at 107, 109 so that the opposingextremities of core portions 102, 104 overlap each other by a distance"x", when the jaw 52 is in closed clamping position. With the coreportions 102, 104 overlapping each other air gaps 111, 113 are definedat the overlapping areas through which magnetic flux is coupled from onecore portion to the other. The lower core portion 104 is secured to theclamping block 132 and is therefore movable along with the opening andclosing mechanism shown in FIGS. 13 and 14. Since the lower core portion104 is attached to the opening and closing mechanism, the lower jaw 52may be employed on a range of conductor diameters, yet the magneticproperties of the air gaps remain unchanged because the areas of the airgaps remain constant regardless of the position of the lower coreportion 104. The outer extremities of the core portions 102, 104 includetapered surface areas 106, 108, respectively, which function toslideably engage the opposite ends of the core portions, therebyautomatically aligning the end of the core portions to assure that tightmagnetic coupling occurs between the core portions. When the lower jaw52 is closed on the conductor 32, the magnetic flux passes from theupper core portion 102 to the lower core portion 104 via an air gap 111contained in the cover sleeve 36 and then passes from core portion 104into core 102 via air gap 113 defined within the column 40. Thisarrangement requires that each core portion 102, 104 consist of stackedlaminations of non-oriented flat rolled electrical steel so that thelaminations of each core portion are parallel to one another in the airgap areas. The inside cross-sectional area of the core cover sleeve 36allows precise alignment of both core portions 102, 104 with theirlongest dimension adjacent the air gaps 111, 113. This ensures properalignment and a tight air gap (FIG. 13a). Additionally, the core coversleeve 36 prevents the core portions 102, 104 from producing corona andprotects the air gap from the environment. The electronic components andtransmitter of the unit 32 are powered from the current flowing throughthe conductor 32 when such current exceeds a threshold value which istypically between 120 to 150 amperes. This relatively high value ofprimary current is not limiting as a practical matter since, during zerowind conditions (worst case) the conductor temperature cannot bedistinguished from ambient temperature when 200 amperes is applied to a1 inch diameter conductor. The threshold value of current can be loweredfor smaller conductor sizes by reducing the number of turns on thesecondary winding of the power transformer coil 100.

The power supply for the unit 30 includes the transformer previouslydiscussed (consisting of the core 102, 104 and coil 100) a diode bridge(FIG. 28), a solid state switching network and two large electrolyticcapacitors 118 for storing a portion of the energy derived from thetransformer secondary. As will be discussed later in more detail, theswitching network senses the DC output of the diode bridge and shortsout the secondary winding of the power supply transformer when thevoltage on the secondary of the diode bridge reaches a preselectedvalue. A test receptacle 204 (FIGS. 7, 10 and 28) mounted within thehousing half 34b between the jaws 50 and near the column 40, providesmeans for powering the unit for testing, calibration, etc.

Attention is now directed to FIGS. 15, 16, and 17 which show a core 128similar to that shown FIG. 12 but which is formed from wound laminationsof oriented steel. With this arrangement, the lower core portion 104must move with respect to the jaw opening and closing mechanism. A coreof this type may be easily formed by winding electrical strip steel overa mandrel and requires less time to manufacture than the stackedlaminated cores shown in FIGS. 10 and 12. The core 128 is formed bycutting the wound "O" shaped laminations and lapping the cut ends tocreate a small air gap. The lower portion 128a of the core 128 isshiftably mounted on a clamping block 146 of the opening and closingmechanism by means of a pair of spaced apart compression springs 150.The lower core portion 128a is held in alignment with upper core portion128b by placing the lower core portion 128a to the right of the centerline (FIG. 15) of the core cover sleeve 36 and clamping a core key 152on the the lower core portion 128a adjacent the clamping plates 153. Oneside of the core key 153 consists of an electrical insulating materialto eliminate a shorted turn around the core 128. The springs 150 arereceived within cylindrical spring holders 148 which in turn arethreadably received in the clamping block 146. Rotation of springholders 148 adjusts the force created by the springs 150 so that thelower core portion 128a is held firmly against the underside of theretainer stop 136; in this manner, the lower core portion 128a ismaintained level. Once the two halves of the core 128 are together and amagnetic flux flows therethrough and between the air gaps 127, it is nolonger necessary for the springs to force the core portions togethersince the magnetic attraction provides the necessary attactive force.

The RF antenna 13 of the sensor-transmitter unit 30 functions both totransmit radio signals at the appropriate frequency, for example in theUHF band and forms a guide for receiving the hot stick tool 166.Additionally, the antenna tube 46 functions to laterally support theunit 30 in a vertical position when the hot stick tool 166 is employedto install or remove the unit 30. The antenna 13 is essentially a halfwave dipole grounded at its center. The center of the driven element isnot intermediate at the ends of the tube 46, but rather is at the base45. Since there is no RF voltage at the center of the half wave dipole,the outer conductor of the coaxial cable from a later discussed UHFtransmitter is grounded at the top of the antenna.

The inner conductor, carrying the RF current is tapped out on the drivenelement at the matching point using bronze sphere 74 or a matching tap.The inductance of the copper arm 72 is tuned out by means of a tuningcapacitor 206, resulting in electrical balance. Both the point ofcontact with the driven element and the value of the capacitor 206 areadjusted for zero reflected power. The capacitor 206 is made variableuntil the antenna 13 is tuned and then is left as a fixed value. The arm72 is insulated from the housing 35 by means of a nylon bushing 73. Thecapacitor 206 and arm 72 could be combined into a single assembly withthe arm 72 being attached to the driven element by the matching tap andthe arm sliding inside a sleeve connected to the inner conductor of thecoaxial cable. Once the match is obtained, the voltage across thecapacitor 206 is low, therefore insulation is no longer a problem. Sincethe RF current is high between the arm 72 and the driven element, thematching tap is constructed from a bronze sphere 74 which attaches thearm to the driven element by means of a brass machine screw 75 so as notto create a source of corona. The side of the bronze sphere 74 adjacentto the driven element fits the contour of the 2 inch aluminum tube 46and ensures a permanent high conductivity connection. Because of thesmooth shape of the matching tap and its close proximity to the antennabase 45, no corona sources are produced with this matching device. Thesphere 48 at the bottom of the tube 46 is hollow and can be formed ofaluminum. The sphere 48 functions to eliminate sources of corona fromthe antenna 13.

The method of matching the antenna element is based upon the fact thatthe impedance between any two points along a resonant antenna isresistive. The antenna length is first adjusted for approximateresonance which for the UHF band is about 6.5 inches. The distancebetween the surface of the antenna 13 and the arm 72 is set atapproximately 0.25 inches to minimize corona. The matching tap is thenadjusted up or down while maintaining the same lateral distance from theantenna until the standing wave ratio is as low as possible. When theseries capacitor method of reactance compensation is used, variouspositions of matching taps are tried after the resonant length of theantenna is established. For each trial matching tap position, thecapacitor is adjusted to achieve minimum SWR (standing wave ratio) untilthe standing waves are reduced to the lowest value. The SWR for theillustrated design is nearly 1:1.

The antenna 13 is held in place with two dowell pins 45a secured to theantenna base 45, as shown in FIG. 10. When the housing halves 34a, 34bare assembled together, the dowell pins 45a extend into both housinghalves 34a, and 34b. This arrangement provides for secure mounting ofthe antenna 13, yet facilitates easy assembly and disassembly.

This simple antenna design possesses a number of advantages. First, itis applicable to a broad band of UHF frequencies, provides a horizontalomnidirectional radiation pattern, transmits signals to a receiver up toa distance of between 6 and 10 miles, and its rugged construction allowsit to be used as a guide for a hot stick tool. In addition, the antenna13 is corona protected and grounded at a power line frequency of 60hertz.

As will be later discussed, the corona sphere 13 may be adapted for usein sensing wind velocity and direction.

The housing 34 is well ventilated by virtue of the access holes 67, aventilation hole 54 in housing 34 and ventilation slots, 110, 112 in theassociated housing halves 34a and 34b. Ventilating air enters the holes54 then passes through the louvers 68, enters the compartments 58 and 60to cool the electronic components therein, is diverted by plates 78a,80b and finally exits through the ventilation slots 110 and 112 which,as best seen in FIG. 8, are angled downwardly so as to prevent ambientmoisture from entering the housing 34 therethrough.

The unit 30 is normally installed at midspan of the conductor 32 sincethe wind velocity will usually be lower at the lowest point on theconductor 32. However, the wind may be lower at other locations, sincetrees, irregular terrain and obstructions may shield the conductor 32 soas to operate at higher temperatures than at midspan. In any event, theunit 30 may be mounted at an appropriate location along the transmissionline 32 without the need for interrupting the current therethrough.Before installing the unit 30 on the conductor 32, it is important toclean the conductor 32 and apply an aluminum conductive grease theretosince transmission line conductors normally become oxidized ratherquickly even in clean environment.

A suitable clamping device 180 mounted on the end of an insulated rod orhot stick 182 may be used to assist in the installation of the unit 30on the conductor 32. The opening and closing wrench 166 may then beinserted into the antenna tube 46 until the transverse pin 137 on thelead screw 138 is in the bottom of the slot 170 of wrench tool 166. Withthe lower jaw 52 in a fully open position, hot stick 172 is used to liftthe unit 30 onto the conductor 32 by passing through opening 37 untilthe upper jaws 50 rest upon the conductor 32. The lead screw 138 is thenturned in order to move the lower jaw 52 upwardly into contact with theconductor 32. At this point, the conductor 32 is tightly gripped betweenthe jaws 50, 52 and the unit is secured in place. Once the weight of theunit is transferred to the conductor 32, hot stick 182 may be removed.The purpose of the horizontal groove 168 in the tool 166 is to engagethe transverse pin 137 so that the tool 166 does not accidently fall outas long as it is turned in a clockwise direction. To release the tool166 from the transverse pin 137, the tool 166 need only be turnedcounter clockwise slightly, and thereafter the tool 166 may be removed.

As shown in FIGS. 4, 4a, 4b, 6, 6a and 7, a solar radiation sensor 124may be optionally provided in order to measure the solar radiationimpinging on the surface of the transmission line 32. The radiationsensor 124 may comprise eight silicon solar cells 123 assembled in anarray and mounted on the top of a raised section 310 on the extension42, immediately above the power supply compartment 42a. The 1 cm by 2 cmsilicon solar cells may be obtained from Sensor Technology, Part No.ST-100. Silicon cells are preferred since they respond to wave lengthswhich represent most of the energy from the sun and also possess highconversion efficiency, temperature stability and lack of fatigue. Thecells may be connected in parallel and shunted with a low valuecalibrating resistor, or connected in series with each cell shunted witha resistor to maintain the cell output to a voltage less than 100millivolts. When the cells are electrically connected in parallel, eachcell operates as an independent current source whose output varieslinearly with light intensity. The low load resistance allows the solarcells to respond quickly to transient conditions (clouds passing) andnullifies changes in cell output due to ambient temperature variations.

The solar cells are mounted in an aluminum enclosure 125 or otherelectrically conductive, electric field shielding material. The cellsare completely encapsulated in a clear silicon potting compound 241which minimizes solar radiation reflections and electrically insulatesthe cells from the aluminum housing 125, and the special glass cover 126overlying the cells 123. The potting compound serves as a thermalbarrier to protect the cells from heat being trapped in an air layerbetween the cells 123 and glass cover 126. The glass cover 126 maycomprise Nesatron glass which is coated with electrically conductive tinoxide, such as that available from PPG Industries. The glass cover 126eliminates the corona or electrical discharge from the surface of thesolar cells 123 while the cell is operating in the high electric fieldof a transmission line. The glass cover 126 is chamfered around itsperimeter at an angle of 45 degrees and is cemented to the aluminumsolar cell enclosure 125 with an electrically conductive material 242.Thus, the corona current, created by the presence of high voltage on theglass 126, flows along a path on the outside surface of the glass andthrough the electrically conducting cement to the enclosure 125 and thento ground, rather than from the enclosure 125 through the cell 123 toground. Since the inside surface of the glass cover 126 is alsoelectrically insulating, the cell 123 is not subjected to currentscapable of causing cell failure. The electrically conducting materialnot only bonds the glass cover 126 to the enclosure 125, but also allowsfor differences in the thermal expansion and contraction between thealuminum and the glass. It should be noted here that the cells 123 couldalso be shielded by a fine electrically conducting screen which iselectrically insulated from the cells but is bonded electrically to thealuminum enclosure 125. The cells 123 are laterally spaced from thewalls of the aluminum enclosure 125 so that the cells are fullyilluminated by the sun when the sun rays are 18 degrees above thehorizon on the back and front of the enclosure 125 and are 16 degreesabove the horizon on the sides of the enclosure 125.

As shown in FIG. 15, an additional sensor 243 may be provided in theunit 30 for sensing the magnitude of the current in line 32 in order tocompute real-time thermal ratings. However, the conductor current isusually measured and recorded at the line termination point, i.e.,station or substation, therefore it may not be necessary to measure linecurrent with sensor-transmitter unit 30. Measuring line current with theunit 30 is convenient in those applications where the units areperiodically moved from one line to another, and it eliminates the needfor installing signal conditioning circuitry to convert the highcurrents from station current transformers to low level signal outputs.The power supply transformer of the unit 30 cannot be used to monitorthe line current, because the secondary winding is periodically shortedby the switching network. However, a current sensing circuit maybeprovided for sensing the charging time for the capacitors 118 since thischarging time is directly related to the magnitude of the line current.Alternatively, an unswitched secondary winding 243 may be added to thepower supply transformer core 128 (FIG. 15). The output of this currenttransformer may be delivered to a hall effect device current tranducer,such as that manufactured by Scientific Columbus, Model 4034; thisdevice provides a linear DC output proportional to the line currentwhich may then be converted to a DC voltage by shunting a resistoracross its output.

A sensor in the nature of an inclinometer 84 may be provided to measuremagnitude of sag of the conductor 32. The inclinometer 84 measures theslope angle of the conductor 32 at the point of attachment of the unit30 to the conductor 32 and calculates the conductor sag from computeralgorithms which describe a typical catenary curve. One suitableinclinometer is manufactured by Schaevits, model LSOC-30. Theinclinometer 84 is self contained, magnetically shielded and is designedto be operated from a 15 volt DC power supply. The output of theinclinometer 84 is an analog DC signal which is directly proportional tothe sine of the angle of tilt. The inclinometer 84 is mounted with itssensitive axis parallel to and above the conductor 32. Because thesensitive axis of the inclinometer 84 is positioned between the twoupper clamps 50, small changes in angle created by strong winds blowingparallel to the conductor and perpendicular to the right or left side ofthe unit 30 will only marginally affect the measured sag. The device 30accurately measures the actual sag with the wind blowing transverse tothe conductor 32 since the sensitive axis will not be affected byrotation of the unit 30 about the axis of the conductor 32.

The angle θ measured by the inclinometer 84 is the angle between apendulum and a line perpendicular to the conductor 32. This angle isused to calculate the sag in accordance with the equation: ##EQU3##where the constant "a" is the ratio of the horizontal component ofconductor tension to the distributed conductor weight per unit length;the quantity may be easily calculated by measuring the sag and the angleof inclination when the device in installed on the conductor. The aboveequation may be used for calculating the sag for a level conductor span,however sag can also be calculated when the points of attachment of theconductor 32 are at different elevations above ground.

The inclinometer 84 is easily calibrated while the line 32 is energizedby using the adjustment screw found on the front of the unit 30 and ascrew driver attachment on the hot stick; this feature improves theaccuracy of the inclinometer 84, in that a differential inclinationmeasurement can be made using the existing transmission line sag as thezero reference angle. This is accomplished by providing a mechanicalzero adjustment which orients the inclinometer so that zero volts isoutput when the unit 30 is on the conductor 32. The gain of theelectronic circuit used to process the signal is chosen to providefull-scale output indication for the maximum calculated change inconductor slope angle to be expected on a particular span.

Attention is now directed to FIGS. 18 through 21 and 26 which depictmeans for sensing the velocity and direction of wind flowing over thethe monitored conductor 32. As described earlier, the present systemuses the parameters of conductor temperature, conductor current, ambienttemperature and solar radiation to define the thermal state of theconductor. However, the conductor has a thermal time constant, thus theexisting conductor temperature is dependent upon the wind velocity anddirection, ambient temperature, solar radiation and line currentconditions which occur typically, 5 to 10 minutes earlier. Measurementof wind velocity and direction on a real-time basis is important sincethese parameters may be quite variable in contrast to ambienttemperature and solar radiation which are rather stable and producesmall changes in the conductor temperature. Therefore, if the windvelocity and direction are measured, then more accurate future conductortemperatures can be predicted or forecasted. Real-time measurement ofthe wind velocity and direction is also useful for predicting theoccurence of conductor vibration and galloping, and the unit 30 can beused to measure the amplitude of the galloping since it also measuresconductor sag.

The wind sensor comprises a plurality of small, electrically heated wireelements 160 which are circumferentially spaced around the longitudinalaxis of the antenna tube 46 in a manner which exposes the wire elements160 to the free stream of air uninterrupted by the unit 30, but protectsthe wire elements from corona. The wire sensors 160 typically may rangefrom 0.00015 to 0.0005 inches in diameter and 0.040 to 0.080 inches inlength. A later discussed circuit supplies a controlled quantity ofelectrical current to heat the sensing elements 160 and thereby maintainthem at constant temperature regardless of wind speed. In order toshield the sensing elements 160 from the high electric field produced bythe conductor 32 without affecting the free stream of air flowing pastthe sensing elements 160, a novel mounting arrangement is provided whichwill now be described. The corona reducing antenna sphere is dividedinto an upper half 154 and lower half 156 which are spaced apart fromeach other to form a circumferentially extending, horizontal opening158. A pair of parallel, spaced apart, annular mounting plates 157 arerespectively secured to the sphere halves 154, 156 within the opening158. As best seen in FIG. 21, a plurality of circumferentially spacedscrews 162 and sleeves 164 connect the mounting plates 157 with eachother and thereby mount the lower half of the sphere 156 to the upperhalf 154. The sensing elements 160 extend through the mounting plates157 and are spaced at 90 degree intervals relative to each other inorder to sense air flowing through the space 158 from differentdirections.

It is important that the air space 158 not be too small since the freestream of air flow over the sensing elements 160 will be disrupted,however, the space 158 should not be too large since the sensingelements 160 could be damaged by corona. The spacing 158 between themounting plates 157 as well as the radial spacing of the sensingelements 160 from the central axis of the tube 146 will vary dependingupon the voltage level of the transmission line and the desired accuracyof the wind velocity measurement within a specific range thereof. Asshown in FIG. 18, shrouds 163 are provided adjacent each sensing element160 in order to shield these elements from electric fields as well asfrom heavy rain or sleet.

The sensing elements 160 are connected by lines 166 to a later discussedbridge circuit. The leads 166 extend upwardly along the tube 46 into thehousing 35 and are protected from corona by a shield 165.

A single horizontally oriented sensing element 160 will provide anindication of the wind cooling velocity on the conductor, but will notprovide an indication of wind direction. Both wind velocity anddirection may be determined by employing two sensing elements 160 whichare oriented in a cross or "X" pattern so that the components of theoutput voltage from the sensing elements 160 will be indicative of boththe direction and magnitude of the wind. The stainless steel cover 165is placed over the sensor element leads 166 to shield the leads from themagnetic fields. Alternatively, the sensing elements 160 may be mountedon top of the raised portion 310 of the upper extension 142.

In the preferred form of the invention, a constant temperature typesensing circuit is employed in connection with the hot wire sensingelement 160, including a feedback loop. Current flow is measured by theheat loss from the hot wire element 160 which has a low thermal inertia.A sensing probe containing hot wire element 160 forms one leg of abalanced wheatstone bridge indicated at 188 in FIG. 26. Any change inthe resistance element 160 caused by cooling due to the wind immediatelyproduces an out-of-balance voltage in the bridge 188. This voltageunbalance is passed through a high gain operational amplifier 184 whichincrements the supply voltage V until balance is achieved. If theamplifier 184 has sufficient gain it will maintain its inputs close to abalanced condition. Any change in the resistance of the sensor 160 willbe corrected by a decrease or increase in the current through the sensor160. The output is the voltage output of the amplifier 184, i.e., thevoltage required to drive the current through the sensing element 160.The voltage across the bridge 188 is directly proportional to thecurrent through the sensor 160, and the power is equal to I² ₂ R₂,consequently the square of the voltage at the top of the bridge isdirectly proportional to the heat transfer between the sensor 160 andthe ambient environment. The wind velocity is proportional to theeffective cooling. Since the ambient temperature of the wind variesbetween calibration and measurement, the influence of temperature on thesensing elements 160 must be considered. The correction for ambienttemperature changes is easily accomplished since the ambient temperatureof the air flow is already being measured by the sensor 86. The windflow data is corrected by comparing calibration data taken at differenttemperatures with the measured ambient data.

Attention is now directed to FIGS. 27 and 28 which disclose in moredetail the electronic components forming a part of the sensortransmitterunit 30. Referring to FIG. 27, the transmitter electronics 192 (FIG. 28)comprises a voltage-to-frequency converter 196, a divider 198 and afrequency shift keyed (FSK) modulator 200. The temperature signalconditioning circuit 186 functions to convert the information from thethermocouple or intergrated circuit temperature transducer forming thetemperature sensor 88 to an analog signal which is proportional to thetemperature of the conductor 32.

The voltage-to-frequency converter 196 may comprise, by way of example,a National Semiconductor LM 131 and produces an output pulse train whichis proportional to the input voltage applied thereto by the signalconditioning circuit 186. The divider 198 may comprise a Motorola ModelMC 4020 and reduces the frequency of the signal output from theconverter 196 to 1/16th of it original value. The FSK modulator 200 is aconventional item employed in transmitting data over telecommunicationlinks and functions to generate modulating frequencies which ensureexact reproduction of the transmitted signal. The UHF transmitter 194 isalso a conventional device such as a two watt Repco 819-series or aMotorola CISCO.

The conditioned signal indicative of the temperature of conductor 32 isdelivered to a digital display 78 which may be of the LED or LCD type.In a similar manner the ambient temperature sensed by sensor 86 isdisplayed on a display 80. As best seen in FIG. 8, the displays 78, 80are mounted in the sides of the housing halves 34a and 34b and areangled downwardly so as to be viewable from below the unit 30. Theconductor temperature signal is processed by the transmitter electronics192 and is delivered to the transmitting antenna 13 through transmitter194 and a tuning capacitor 206.

The electronic circuits for the unit 30 which monitor the temperature ofthe conductor 32 are mounted on a plurality of printed circuit boards(PCB's) which in turn are secured to the inner faces of cover plates 62and 64. As shown in FIG. 28, an electrical circuit forming part of thepower supply is defined on a printed circuit board 190 which in turn isconnected with power supply transformer 100. The electronic circuitforming a part of a UHF transmitter 194 is mounted on a second printedcircuit board 192. PCB'S 190 and 192 are mounted on the interior face ofthe cover plate 64. A temperature signal conditioning circuit 186 isconnected with the temperature sensor 88 and is mounted on cover plate62 along with a UHF transmitter 194.

The power supply for the unit 30 provides a relatively constant voltageand power to the electronics even though the primary current in theconductor 32 may range from 100 to 2000 amperes under steady-stateconditions and 20,000 to 30,000 amperes for transient conditions. If thesecondary of the transformer was open circuited, all primary current inthe conductor 32 would become magnetizing current and the transformercore would be driven into saturation, thus producing very high secondaryvoltages, typically several thousand volts. Conversely, if the secondaryof the power supply transformer 100 was not open or short circuited, theexcess power at high primary currents would cause excessive heating ofthe core and coil, and consequently errors in the measured conductortemperatures. The present invention employs a switching network whichonly allows a predetermined power and voltage to be derived from thepower supply transformer.

The power supply for the unit 30 broadly comprises the power supplytransformer 100, a diode bridge 202, solid state switching network and apair of electrolytic capacitors 118 to store a portion of the energyderived from the transformer secondary. The diode bridge 202 and solidstate switching network are defined on the PCB 190. The power supplyswitching network senses the DC output of the diode bridge 202 andshorts out the secondary winding of the power supply transformer 100when the voltage on the secondary of the diode bridge 202 reaches afirst value. When the voltage across the capacitors 118 drops to asecond value below the first value, the switching network unshorts thewinding and allows the voltage again to climb to the first value. Thisprocess repeats itself and results in the storage of energy in thecapacitors 118, which in turn supply the electronics and the transmitter194 with a relatively constant DC voltage and power, and the transformercore thus never saturates even for high values of line current.

In order to provide power to the unit 30 when it is disconnected fromthe conductor 32 for purposes of calibration checks on the varioussensors or the like, a suitable AC voltage source may be connected withthe test receptacle terminals 204, which are in turn connected to thesecondary of the transformer 100.

Attention is now directed to FIG. 29 which diagrammatically depicts theuse of a plurality of the sensor-transmitter units 30 in a system formonitoring a 40 mile length of transmission line 32. Four of thesensor-transmitter units 30 are mounted on each of a series of three tofive mile stretches. The forty mile transmission line 32 is divided upinto four zones of ten miles each which include 8 of the units 30,frequencies (F₁ -F₈). Sensor-transmitter units which are dedicated tosensing conductor temperature are indicated as connected to the line 32with a dot while units capable of sensing multiple parameters such asambient temperature, conductor temperature, solar radiation, current,wind and conductor sag are indicated by an encircled dot. Zones 1 and 4include a UHF receive/transmit repeater which is powered from acapacitive voltage transformer (CVT) connected to the line 32, whileZones 2 and 3 include UHF receivers powered by a CVT connected to line32. A UHF receiver 208 is connected at each end of the line 32.

Data from the sensor-transmitter units 30 may be transmitted usingdifferent UHF frequencies (F₁, F₂. . . F₃) or a single frequency. Theprocessing electronics for those units 30 which sense multipleparameters is capable of coding a digital signal with seven multiplexedinputs into a frequency shift keyed audio tone. The unit seriallytransmits between 1 to a maximum of 7 channels of information on onefrequency. The input signals are processed for any necessary gainchanges and are then multiplexed. The analog multiplexer selects eachchannel of an analog input in sequence on command from an encoder. Eachselected analog channel is then digitized by the analog-to-digitalconvertor and is transferred in digital form to an encoder. The encodeddigital signal is then converted to audio frequency shift tones by thefrequency shift transmitter. An appropriate matching pad is installedbetween the FSK transmitter output and the input to the UHF transmitter.An expander is necessary only when multiple units are used on the samefrequency.

The input parameters from each unit 30 may be separated by usingdifferent RF carrier frequencies for groups of transmitters. In thosecases where it is difficult to obtain the required number of licensedfrequencies, time sequencing, that is sychronizing to the power linefrequency, is an alternative approach to transmitting the informationand is the preferred method for separation between units on the samecarrier frequency. Receiving stations "A" and "B" are positionedadjacent the respective ends of the transmission line 32. The data fromthe units 30 may be transmitted to these stations in any of severalways. Those units 30 within approximately five miles of thecorresponding station at the end of the line 32 may transmit directly tothe UHF receiver associated with that station. Those units 30 withinZones 1 and 4 which are six to ten mile away from the station maytransmit to a UHF repeater installation. If only one UHF frequency isused for all of the units 30, then another frequency is required for therepeater station. The units 30 within Zones 2 and 3 transmit UHF signalsto a power line carrier (PLC) installation which injects the timesequenced signals into the transmission line phase wire or conductor 32,through the use of the capacitive voltage transformer (CVT). The CVTalso provides power to the UHF, receiver/PLC transmitter by capacitivecoupling to the phase wire. Signals may also be injected using PLCtechniques with the ungrounded shield wire mounted on top of thetransmission line structure. The advantage of this method is thatequipment maintenance can be performed without the transmission linebeing shut down.

Reference is now made to FIG. 30 which depicts the overall componentparts of the system of the present invention. The sensor-transmitterunit 30 which senses conductor temperature and up to 7 parameterstransmits signals to a UHF receiver 208 which typically may be locatedin a power substation along with a multiplexer/scanner 210 as indicatedpreviously, alternatively however, these signals may be transmitted tothe substation using PLC signals through the transmission line 32itself. Additional sensor-transmitter units 30 along the line 32 mayalso transmit real time data relating to conductor temperature, ambienttemperature, solar radiation, wind velocity and direction, conductorcurrent and line sag to the substation location, or alternativelyconductor temperature may be monitored on the line while ambienttemperature, solar radiation, wind velocity, wind direction and linecurrent data may be obtained directly at the substation using one of theunits 30 or a remote weather station if the line is short. The real-timedata received from the units 30 at the substation is scanned at apreselected rate, converted from analog to digital form and is thenmultiplexed to a systems operation center via any suitabletelecommunication link such as telephone, microwave, etc. The datareceived through the communication link at a systems operation center isinput to a dynamic line capacity computer which may comprise by way ofan example a microcomputer system 214 that performs real-timecalculations using the received data. The computer 214 includes aspecial software program for performing the calculations, a simplifiedflow chart for the program being shown in FIG. 31. The computer 214first determines the validity of the data at 216 and employs atransmission line data file 218 in order to first determine at 222 thesafe capacity for each monitored span of the transmission line 32. Thespan of the transmission 32 with the lowest computed current iscalculated at 224 and is identified as the "critical span". Havingidentified the critical span, the resultant calculated current becomesthe maximum transmission line capacity. The computer operator can thenselect load levels higher than the steady state capacity for the"critical span" and direct the computer 214 to predict at 226 the timerequired for this span to reach its safe conductor temperature. Theseload levels may be greater or less than the design rating thereof. Usingthe computer 214, the operator can determine when loads greater thandesign rating can be carried safely, or conversely, when loads less thanthe design rating cannot be carried without exceeding the safe conductortemperature. This feature becomes the distinct advantage for theoperator during major system outages; knowledge of the thermal state ofthe transmission line can prevent opening lines unnecessarily andweakening the transmission grid. The monitored and calculated data isconverted to graphical form at 228. Graphical display of the data may beachieved using a hard copy printer 234 or CRT 236 shown in FIG. 30. Datafrom a conventional rating file 220 may be combined with the dataidentifying the critical span at 224 to form a capacity table 232,similarly, the critical time calculated at 226 may be employed to createa critical time table 230. Operating data may be permanently stored on amagnetic tape recorder 238, floppy disc 240 or other suitable storagemedia (FIG. 30).

For purposes of providing a complete description of the presentinvention, reference is made to a listing of one suitable program foruse in the present system which is contained in an Application forCopyright Registration filed in the U. S. Copyright Office on Jun. 13,1984 and identified by Certificate of Copyright Reg. No. TXa 169-608,the entire contents which is hereby incorporated by reference herein.

In view of the foregoing, it is apparent that the system described abovenot only provides for the reliable accomplishment of the objects of theinvention but does so in a particularly effective and economical manner.It is recognized, of course, that those skilled in the art may makevarious modifications or additions to the preferred embodiment chosen toillustrate the invention without departing from the spirit and scope ofthe present contribution to the art. Accordingly, it is to be understoodthat the protection sought and to be afforded hereby should be deemed toextend to the subject matter claimed and all equivalents thereof fairlywithin the scope of the invention.

I claim:
 1. A method for monitoring the current carrying capacity of alength of an overhead electrical power line which includes a pluralityof overhead electric power line spans, comprising the steps of:(a)monitoring on a real-time basis at least the actual conductortemperature parameter of said overhead electrical power line along atleast one span, and using the monitored actual conductor temperatureparameter to calculate the surface coefficient of heat transfer on saidat least one monitored span; (b) generating data signals at said atleast one monitored span corresponding to a desired maximum conductortemperature and said surface coefficient of heat transfer; (c)determining the current carrying capacity of each overhead electricpower line span using at least the data signals generated in step (b);and (d) identifying the overhead electric power line span having thelowest current carrying capacity determined in step (c).
 2. The methodof claim 1, wherein the generated data signals relative to each span aretransmitted to a receiving station, multiplexed, then transmitted to anoperating station; and thereafter, determining the particular span alongsaid line having the lowest current carrying capacity using themultiplexed data transmitted to said operating station.
 3. The method ofclaim 1, wherein said line spans are divided into a plurality of zones,including a near zone within radio transmission range of a receivingstation and a far zone beyond radio transmission range of said receivingstation, and data is transmitted from said near zone to said receivingstation by radio wave transmission; and data is transmitted from saidfar zone to said receiving station through said power line.
 4. A methodfor monitoring the current carrying capacity of a length of an overheadelectrical power line which includes a plurality of overhead electricpower line spans, comprising the steps of:(a) monitoring on a real-timebasis at least the actual conductor temperature parameter of saidoverhead electrical power line along at least one span; (b) monitoringon a real-time basis one or more ambient conditions, said one or moreambient conditions affecting the current carrying capacity of thecorresponding overhead electric power line spans; (c) monitoring on areal-time basis the line current of the power line; (d) generating datasignals at the monitored spans including using at least the monitoredactual conductor temperature, the monitored ambient conditions and theline current to calculate the surface coefficient of heat transfer; (e)determining the current carrying capacity of each overhead electricpower line span using at least the calculated surface coefficient ofheat transfer and a desired maximum conductor temperature; and (f)identifying the overhead electric power line span having the lowestcurrent carrying capacity determined in step (e).
 5. The method of claim4, wherein said one or more ambient conditions are monitored at aweather station remote to said certain spans.
 6. The method of claim 4,wherein the step of monitoring the current is performed by measuring thecurrent flow through said overhead electric power line at the end ofsaid overhead electric power line.
 7. The method of claim 4, wherein thestep of monitoring the current is performed by measuring the currentflowing through one overhead electric power line span and generatingdata signals in response thereto.
 8. The method of claim 4, wherein thesag of said overhead electric power line is also monitored along atleast one span of the length of said overhead electric power line andused to determine said maximum conductor temperature, with data signalsgenerated in response thereto.
 9. The method of claim 8, wherein saidmonitoring step is performed by continuously sensing the slope of saidoverhead electric power line along said one span and data signalsgenerated in response thereto.
 10. The method of claim 4, wherein thecurrent flow in the span having the lowest temperature is increased toincrease the temperature of said span sufficiently to prevent theformation of ice along the entire length of an overhead electric powerline.
 11. The method of claim 4, wherein the generated data signalsrelative to each span are transmitted to a receiving station,multiplexed, then transmitted to an operating station; and thereafter,determining the particular span along said line having the lowestcurrent carrying capacity using the multiplexed data transmitted to saidoperating station.
 12. The method of claim 4, wherein said line spansare divided into a plurality of zones, including a near zone withinradio transmission range of a receiving station and a far zone beyondradio transmission range of said receiving station, and data istransmitted from said near zone to said receiving station by radio wavetransmission; and data is transmitted from said far zone to saidreceiving station through said power line.
 13. The method of claim 12,wherein the data in said far zone is first transmitted to a radioreceiver within radio transmission range of said far zone, andthereafter, transmitted to said receiving station through said overheadelectric power line.
 14. The method of claim 12, wherein the data insaid near zone is first transmitted to a radio receiver within radiotransmission range of said receiving station and thereafter, radiotransmitted to said receiving station.
 15. The method of claim 1,wherein the sag of said overhead electric power line is also monitoredalong at least one span of the length of said overhead electric powerline and used to determine said maximum conductor temperature, with datasignals generated in response thereto.
 16. The method of claim 4,wherein the generated data signals relative to each span are transmittedto a receiving station, multiplexed, then transmitted to an operatingstation; and thereafter, determining the particular span along said linehaving the lowest current carrying capacity using the multiplexed datatransmitted to said operating station.
 17. The method of claim 5,wherein the generated data signals relative to each span are transmittedto a receiving station, multiplexed, then transmitted to an operatingstation; and thereafter, determining the particular span along said linehaving the lowest current carrying capacity using the multiplexed datatransmitted to said operating station.
 18. A method as recited in claim1, wherein the desired maximum conductor temperature for the span isdetermined by measuring the actual sag of the span, and step (c)includes using the equation: ##EQU4## wherein Q_(c) is convected heat,and is determined utilizing the calculated surface coefficient of heattransfer and the desired maximum conductor temperature, Q_(r) is thermalradiation and is measured, and Q_(s) is solar radiation and is alsomeasured, R is resistance, and wherein the above equation is utilized todetermine a maximum I for the span.
 19. A method as recited in claim 1,wherein the equation: ##EQU5## is used in step (a) with a measuredconductor temperature and I to calculate the surface coefficient of heattransfer in step (c).
 20. A method as recited in claim 4, wherein thedesired maximum conductor temperature for the span is determined bymeasuring the actual sag of the span, and step (e) includes using theequation: ##EQU6## wherein Q_(c) is convected heat, and is determinedutilizing the calculated surface coefficient of heat transfer and thedesired maximum conductor temperature, Q_(r) is thermal radiation and ismeasured, and Q_(s) is solar radiation and is also measured, R isresistance, and wherein the above equation is utilized to determine amaximum I for the span.
 21. A method as recited in claim 4, wherein theequation: ##EQU7## is used in step (d) with a measured conductortemperature and I to calculate the surface coefficient of heat transferin step (e).